Recent legislative changes in the United States have promoted competition in the telecommunication industry and spurred demand for new services at lower prices. These trends are pressuring major telecommunications carriers to increase capacity while reducing the cost of providing service. Consequently, major carriers around the world are looking to packet technologies, such as Internet Protocol (IP), frame relay, and Asynchronous Transfer Mode (ATM), to replace circuit-switched technologies in the Public Switched Telephone Network (PSTN) for providing voice capability. In addition, IP, frame relay, ATM, and other packet-based technologies offer narrow-band and broad-band services to selected customers on the same network, providing the same platform for integrated voice, data, and video services from low bandwidth to very high bandwidths.
Over the decades, however, major voice carriers have invested heavily in developing a Signaling System 7 (SS7) signaling and switching infrastructure to offer reliable telephone service. This infrastructure includes countless systems for billing, provisioning, maintenance, and databases that are compatible only with SS7. These systems are commonly referred to “legacy systems,” a term that also includes other proprietary protocols such as ISDN_PR1, DPNSS, ISUP, TUP, NUP, H.323, and SIP. Due to the substantial investment in the legacy systems, it is desirable to keep the legacy systems in operation, yet still take advantage of the newer packet technologies.
Moreover, certain demographic trends are motivating telephone call carriers to integrate their legacy systems with packet-switching networks. Certain countries are known to generate an above-average amount of long-distance telephone traffic. For example, residents of Israel are known to consume long-distance telephone services at a rate far greater than the average of residents in other industrialized nations. Long-distance telephone services carried over the PSTN are expensive. Voice calls carried over the globally accessible packet-switched network known as the Internet, however, are generally free. Accordingly, local telephone companies and other call access providers in certain countries are acutely interested in finding ways to integrate the PSTN with the Internet.
These legacy systems, however, do not handle the protocols for the newer packet-switching networks, and, the newer packet-switching network protocols in common use are incompatible with one another. Therefore, there is a need for signaling protocol that can handle call-control information between gateways that join the PSTN or legacy systems and a packet-switching network, notwithstanding the protocol employed by voice calls arriving at the gateways.